Myeloid cloning assays and both short term and long term hematopoietic suspension culture systems will be used to investigate proliferative and maturation defects in human leukemia. The influence of colony stimulating factors, prostaglandins, retinoic acid and differentiation proteins present in endotoxin serum will be monitored on fresh or culture acute and chronic myeloid leukemic marrow cells, preleukemic marrow and myeloid leukemic cell lines. Differentiation antigens and Ia antigen expression on normal and leukemic progenitor cells will be explored with monoclonal antibodies. The interaction between marrow stromal cells, hematopoietic stem cells and differentiating blood cell types will be analyzed in long term marrow cultures and the process of myelofibrosis further analyzed in vitro.